Hose for low-temperature liquids



March l5, 1966 F. D. BOND, JR., ETAL 3,240,234

HOSE FOR LOW-TEMPERATURE LIQUIDS original Filed Feb. 24, 1960 2sheets-'sheet 1 /NVE/vroRs 24 FRANK D. BOND,JR.

LADlsLAs c. MATscH JAMES A. PRocroR ATTO NEV m'ck i5, g@ F, D, BOND,JR., ETAL 3,240,234

HOSE FOR Low-TEMPERATURE LIQUIDS 2 sheets-'sheet a Original Filed Feb.24. 1960 FRANK D. vBOND,JR. L ADISLAS C. MATSCH JAMES A. PROCTOR UnitedStates Patent O 1 claim. (ci. 13s- 129) This application is a divisionof Serial No. 10,598 filed Feb. 24, 1960, now abandoned.

This invention relates to a llexible hose for transferring low-boilingliquids at temperatures below about 120 C., and more particularly to aflexible, insulated hose for transporting liquid hydrogen, liquid heliumand the like.

When low-boiling or cryogenic liquid transfers are conducted betweenvessels, either or both of which are mobile (or portable), theconnection or rigid transfer piping requires accurate orientation ofequipment in three dimensions. Where such equipment is difficult tomove, it would be advantageous to make the connection by a ilexiblehose.

Heretofore, liquid oxygen and nitrogen have been transferred fromtransport vessels to stationary storage tanks in flexible uninsulatedhoses of large diameter. Such hoses were adequate for this servicebecause the liquids were relatively inexpensive and because thevolumetric flow rates Were high, thus resulting in small percentageevaporation of the total liquid due to heat inleak. However, theexpanding usage of such liquids often far remote from the point ofproduction may greatly increase their value at the point of consumptionand require extreme conservation measures. Furthermore the increasedutilization of more expensive cryogenic fluids boiling below about 196C., as for example liquid hydrogen and liquid helium, has created a needfor flexible transfer hoses which are smaller in size are moreeffectively insulated against heat leak.

A satisfactory flexible hose for such service should possess at leastthe following characteristics:

(1) Structurally safe for processing all atmospheric gases and hydrogen.

(2) Capable of restricting heat leakage to a rate compatible with thecost of the refrigerated liquid handled.

(3) Free from cold spots on the jacket which could present a combustionhazard due to air condensation, a handling hazard, or develop frostsufcient to impede manipulation.

(4) Adequate flexibility and durability at the lowest anticipatedtemperature which is about 4 K., the boiling point of helium atatmospheric pressure.

(5) Minimum cooldown flash-off.

A principal object of the present invention is to provide a highlyefficient, flexible hose for transporting loW- boiling liquids.

Another object is to provide an improved ilexible hose for transportinglow-boiling liquids, which hose is eiliciently insulated to minimize theheat inleak.

Still another object is to provide a method of assembling a flexible,thermally insulated hose for transporting low boiling liquids.

Additional objects and advantages of this invention will be apparentfrom the ensuing disclosure and the appended claim.

In the drawings: i

FIG. l is an elevational view, partly in section, of a flexible hoseembodying the principles of the invention;

FIG. 2 is an isometric view of a composite insulating material employedin the invention and shown in a tlat- "lee tened position with partsbroken away to expose underlying layers;

FIG. 3 is an elevational view, partly in section, of a ilexible hoseembodying the present invention and including an adsorbent-getter space;

FIG. 4 is an isometric View of a cylinder illustrating the rst step ofthe present method for applying flexible, composite heat insulatingmaterial to a curved surface;

FIG. 5 is an isometric view of a cylinder illustrating the final step ofthe present method for applying flexible, composite heat insulatingmaterial to a curved surface; and

FIG. 6 is an' isometric View of a cylinder illustrating the steps of analternative novel method for applying flexible composite heat insulatingmaterial to a curved surface, according to the present invention.

Briefly, one aspect of the invention comprises a hose for transportinglow-boiling liquids including a ilexible corrugated metallic innerconduit, a larger ilexible corrugated metallic jacket beingconcentrically spaced around the inner conduit so as to form anevacuable annular insulation space therebetween, the minimum diameter ofthe flexible corrugated jacket being greater than the maximum diameterof the flexible corrugated inner conduit. The annular insulation spaceis substantially filled with a composite insulating material comprisingalternate layers of radiation impervious barriers and low heatconductive fibrous sheets. In a preferred form, the radiation imperviousbarriers are aluminum foil and the low heat conductive layers arepermanently precompacted sheets of unbonded glass liber paper.

This invention also includes a method for applying alternate layerinsulation in which at least one component of the insulation is providedin strip form and helically wound around a curved surface, the edges ofthe spirals being overlapped to provide a continuous discrete layer ofthe first component between two continuous discrete layers of a secondcomponent.

A corrugated tube is essentially a bellows, and it is wellknown thatWhen such tubes are exposed to a substantial pressure differential, theywill expand or contract as a spring. Furthermore, the forces exerted bysuch corrugated tubes vare considerable even `at such loW pressuredifferentials -as 15 p.s.i. This force can be calculated by multiplyingthe pressure differential times the average cross-sectional area exposedto the P. Thus, a 3inch corrugated tube when evacuated can exert acontracting force of almost lbs. imposing internal pressure on acorrugated tube will cause elongation with a force of similar magnitude.

Based on the foregoing considerations it would logically appear to oneskilled in the art that assembling two such tubes together in concentricfashion and evacuating the space therebetween would cause the outercorrugated jacket -to contract and the inner corrugated conduit tobuckle severely. If a substantial positive pressure considerably aboveatmospheric is now improved by fluid inside the inner corrugatedconduit, it will tend to elongate but being restrained by the outercorrugated jacket, the forces tending to cause buckling will be evenfurther increased. Thus, the entire assembly would appear to be highlyunstable and not at all suitable for a vacuum-insulated structure inwhich the inner and outer walls must not be permitted to touch eachother.

Another critical factor to be considered is the extreme compressionsensitivity of the alternate l-ayer type of insulation. That is, as thelayers are compressed closer and closer together, the solid conductancein the direction perpendicular to layers, increases appreciably. Theabovementioned buckling tendency of the inner conduit would appear toimpose severe localized compression on the alternate layer typeinsulation if the latter is to be employed as a separator and supportfor the concentric corrugated members. Logieally, this would cause areasof high heat conductance at the localized points of compression.

In spite of these enumerated problems, it has been unexpectedly foundthat the particular combination of elernents constituting the presentinvention provides an improved flexible hose for transportinglow-boiling liquids which restricts heat inleak to a very small value,and which retains adequate iiexibility and durability at the lowestanticipated temperature of 4 K.

Referring now more specifically to the drawings and particularly toFIGS. 1 and 2, the present fiexible hose `includes corrugated innerconduit for transporting the low temperature liquid, and corrugatedouter jacket 11 arranged concentrically with an annular space 12`therebetween. The annular space between the two tubes is filled withcomposite insulation 13, and maintained under a vacuum pressure of belowabout 30 microns of mercury.

The corrugated inner conduit 10 and outer jacket 11 may if desired, beexternally covered with wire braid 14a and lib. Where the lowtemperature liquid supply pressure is low, the inner conduit braid maybe eliminated, thus reducing liquid flash-off during cool-down of thehose. The advantage in using wire braid on the inner conduit 10 is thatthe allowable working pressure of the hose may be increased. Theelimination of such wire braid is particularly feasible in smalldiameter hoses. This was demonstrated by tests in which a lsinchdiarneter exible tube without braid was hydraulically pressurized to 250p.s.i.g. Deformation of the hose was found to be linear up to 200p.s.i.g.; i.e., the elastic limit of the hose was not exceeded belowthis pressure. At 250 p.s.i.g., a permanent elongation of 1.6% resulted.Larger diameter corrugated tubes of commercially available thicknessesbenefit more by external wire braid because they cannot withstand asmuch pressure without exceeding the elastic limit.

Stainless :steel is the preferred material for the flexible, corrugatedmetal tubes because of its higher strength and welding convenience.Higher strength results in less mass of metal in contact with the liquidand requires less refrigeration to cool the hose to operatingtemperature. As to welding, the end connections on flexible hoses forcryogenic service are preferably constructed of low-conductive stainlesssteel, and Ithe use of other metals such as bronze for the corrugatedhose would require a dissimilar metal joint between the tube and the endconnection. Dissimilar metal joints are less dependable in high-vacuumservice than homogeneous welds between similar metals.

The corrugated tubing is preferably the seamless type to minimize thepossibility of vacuum leaks which in turn would decrease the insulationefficiency. However, welded corrugated tubing has been foundsatisfactory for use in the present invention, but a mass spectrometric(helium) leak test should be conducted on the tubes before assembly ofthe hose.

Corrugated exible tubing is normally available in two forms: In theannular type illustrated in FIG. l, the corrugations are separate andare formed normal to the tube axis, while in the helical type of FIG. 3the corrugations are pitched and continue in helical form along thelength of the tube. Hoses formed with helical convolutions appear tooffer 75% as much ow resistance as those formed with annularconvolutions. For this reason, the former are preferred in the practiceof this invention.

Highly efficient insulation is important in Iiexible cryogenie hosesbecause it avoids unnecessary loss of valuable low-temperature liquids.Uniformity of insulation is also important in order to avoid localizedcold spots on the hose. Cold spots not only result in increased heatinleak, but may also cause severe burns to operators handling or comingin contact with the hose. Furthermore, air may condense on a cold spot,thus producing a liquid enriched in oxygen which may be hazardous incontact with inflammable materials. High insulating efiiciency coupledwith low density and low heat capacitance are also important incryogenic hoses in order to minimize the loss of expensive refrigerationneeded to cool the hose repetitively to operating temperature. Theseinsulating requirements must be met while preserving flexibility andthinness of the insulating layer.

The present alternate layer insulation provides unexpected advantages invacuum-insulated flexible hoses. As more fully described and claimed incopending U.S. Serial No. 597,947, 824,690 and 4,298, filed respectivelyon July 16, 1956, July 2, 1959 and Jan. 25, 1960, in the name of L. C.Matsch, now U.S. Patents 3,007,596, 3,009,601 and 3,009,600,respectively, the low conductive component is a fibrous insulation 15which can be produced in sheet form. Examples of the latter include afilamentary glass material such as glass wool and fiber glass,preferably having fiber diameters of less than about microns. Also suchfibrous materials preferably have a fiber orientation substantiallyperpendicular to the direction of heat How across the insulation. Asatisfactory material consists of an elastic fluffy web of unbondedfibers having individual liber diameters of 0.2 to 5 microns and woundwith sufcient compression to provide `between 5 and 50 layers per inchthickness. Best results are obtained when the assembled low-conductivefibrous layers are permanently precompacted in an unbonded paper formhaving a density of less than 8 grams per sq. ft. as distinguished fromelastically compressed, web forms and have individual fiber diameters ofless than about 5 microns and preferably between .05 and 1.0 micron. Forbest results from the standpoints of insulating etiiciency and ease ofassembly, the fibrous paper is provided in densities of less than 3grams per sq. ft. Also, such fibers are preferably less than about 0.5inch long, and installed with the radiation-impervious layers so as toprovide a composite insulation under compressive load of less than 0.03lb. per sq. in.

The spaced radiation-impervious barriers 16 of the Composite, alternatelayer insulation may comprise either a metal, metal oxide or metalcoated material such as aluminum coated plastic film, or other radiationreflective or radiation adsorptive material or a suitable combinationthereof. Radiation reflective materials comprising thin metal foils areparticularly suited in the practice of the present invention, and inparticular, reflective sheets of foil, e.g. aluminum, having anuninstalled emissivity of between about 0.005 and 0.2, and a thicknessbetween about 0.2 millimeter and 0.002 millimeter. Aluminum foils havinga thickness between about 0.005 millimeter and 0.02 millimeter have beenfound to give best results. Also, the composite insulation is preferablyapplied so as to provide between about 40 and 250 radiant heatreflecting shields per inch of insulation space cross-section.

The heat leak for small size hoses up to and including 11/2" insidediameter constructed in accordance with this invention and employingaluminum foil-permanently precompacted glass fiber alternate layerinsulation has been found to be between about 1A and 1/2 B.t.u. per ft.-hr. when the insulation jacket pressure is about 0.1 micron. This issubstantially lower than the corresponding heat leak for any known priorart flexible conduits for lowtemperature liquids. For example, in onesuch conduit employing straight vacuum insulation without any type offiller, radiation alone contributes at least 1 Btu. per linear ft. perhr. heat inleak. Other radiation refiective materials which aresusceptible of use in the practice of the invention include tin, silver,gold, copper, cadmium or other metals. When fiber sheets are used as thelowiconductive material, they may additionally serve as a support meansfor relatively fragile radiation impervious sheets.

As previously mentioned, it has been found that the present alternatelayer insulation provides special advantages in vacuum-insulated hoses,particularly the metal foil-fibrous sheet combination. The pressureimposed by the metal foils prevents fibers from dropping into theconvolutions of the metal tubes. Loose fibers or other particulatematerial between the corrugations should be avoided because they wouldabrade the metal, prevent free flexing of the hose, and may overstrainthe corrugations on the inner radius of a bend. Hoses insulated withpowderous materials would be especially susceptible to damage andimproper performance for these reasons.

Another unique advantage of the combination metal foil and fiberinsulation in the present hose is that the foils serve to protect thera-ther fragile iber sheets against damage due to hose fiexure. Withoutfoils the severe abrasion and compression imposed repeatedly on thefibrous insulation by the rough, uneven metal surfaces will soon breakand separate the brittle unbonded fibers. Bare uninsulated areaseventually develop through which the inner conduit and jacket makemetal-to-metal contact with consequent high heat transmission. Thereflective foils absorb the abrasion, distribute the compressive loadsmore uniformly through the insulation, and hold the unbonded fibersevenly distributed in the respective layers.

Still another important advantage of using alternate layer insulation inthe present hose is that such insulation provides an excellentcontinuous spacer to maintain the concentri-city of the liquid conduitwithin its vacuum jacket. No additional spacers or tube separators withtheir attendant heat leak, are required. In previous attempts to providesatisfactory conduits for cryogenic fiuids, the requirement for numerouscentering supports in the vacuum space has added greatly to the cost andcornplexity of manufacture and has penalized the performance of theinsulation. However in the present invention the composite insulationmay serve as the sole centering support for the concentric tubesthroughout the entire hose length between end connections.

Finally the exible insulated conduit of this invention benefits greatlyfrom the relatively moderate vacuum requirement inherent in the highlyeffective, alternate layer insulation. The fine fibers obstruct heattransport by molecular motion of the residual gas and provide goodinsulation performance with absolute pressures to 100- fold higher thanthose required in systems employing straight-vacuum without filler. Thisis an important advantage in cryogenic hoses where extreme vacuums areexceptionally difficult to maintain because of the repetitivetemperature cycling imposed on the unit.

The following Table I lists suitable specifications for various sizeflexible hoses, constructed in accordance with this invention:

In Table I, nominal LD. refers to the minimum internal diameter of astainless steel tube covered with wire braid, and the compositeinsulation consists of alternate layers of permanently precompactedglass fibrous unbonded paper and aluminum shields. The fibrous papersweighed less than 3 grams per sq. fat. and were composed of individualbers having diameters between 0.2 land 0.5 micron, and lengths of belowabout 0.5 inch. Also, the alluminum shields we-re about .0062 mm. thickwith an emis- 6 sivity of about .058. Finally, the insulation wasassembled with a tightness equivalent to Aabout 62 layers of glassfibrous papers per inch thickness. As few as nine layers of insulationhave been used successively, that is, with lbarely discernible coolnessof the vacuum jacket during a liquid hydrogen transfer,

The corrugated tubing used in the present flexible hose may be purchasedas standard commercial items, and the sizes given in the preceding TableI are determined largely by the dimensions of standard tubes availableon the market. In selecting tube sizes for a given assembly, the minordiameter of the jacket should be sufficiently larger than the majordiameter of the inner condu-it to provide ample straight-throughclearance for the insulation.

The insulation space is preferably completely filled with the compositeinsulation to minimize eccentricity between the inner and outer tubesand to maintain contiguous supporting contact between the componentlayers. The total number of insulation layers installed will thereforedepend upon the annular space provided between the tube walls.Preferably the straight-through clearance for insulation should be atleast 0.1 inch and not more than about 0.6 inch. Clearances narrowerthan this range do not provide the requisite number of shields foreffective radiation impedance. Greater clearances contribute onlymarginal insulating value while increasing considerably the heatcapacitive mass to be cooled-down for service. Greater clearances withattendant heavier conduit also penalize unnecessarily the flexibility,lightness and economy of the hose.

The minimum bending radius listed in the last column of Table I is theminimum radius that can be imposed without danger of damage to the hose.These limits are always imposed on corrugated metal tubing regardless ofits use, and no-rmally no precautions are taken to prevent abuse of thehose by bending to a smaller radius. To some extent the wire braid willhelp to restrain the hose from bending beyond the allowable limit. Inthe present hose assembly, the minimum radius is usually imposed by thelarger d-iameter jacket.

Since it is necessary to maintain the annular space between the twoconduits 10 and 11 under a substantial degree of vacuum for highinsulating efficiency, a preferred embodiment includes means `forremoving gases accumulating in suchl space. More specifically, anadsorbent such as crystalline zeolitic molecular sieve material havingpores of about 5 angstrom units in size, may be provided for removingtraces of Water and air, in accordance with the teachings of U.S. PatentNo. 2,900,800 to P. Loveday. Alternatively or in addition to theadsorbent, a hydrogen selective getter such as palladium oxide or silverexchanged zeolite X may be provided for removing hydrogen evolved fromthe surrounding metal surfaces in accordance with U.S. Patent No.3,108,706 in the name of L. C. Matsch et al.

Some services for cryogenic hoses require intermittent or cyclicoperation in which the cold service periods may be of insufficientduration for effective use of an adsorbent. In such cases, an activemetal getter such as barium may preferably be employed to remove allresidual gases with exception of the inerts, in accordance with U.S.Patent No. 3,114,469 in the name of A. W. Francis.

The aforementioned adsorbent-getter systems are illustrated in FIG. 3,and rigid tube 17 is provided at least at one end of the flexible hoseassembly, Tube 17 has about the same diameter as corrugated jacket 11,and is bonded thereto at one end. The annulus at the other end of tube1'7 is sealed to retain the adsorbent by means of a porous plug 18,which for example may be formed of glass wool. The end of corrugatedinner conduit 10 is metal-bonded to inner, rigid end conduit 19, and theouter end thereof is surrounded by thin-walled, tubular connector 2t)having an inner diameter slightly larger than the outer diameter ofinner end conduit 19. One end of tubular connector is flared and joinedto tube 17, and the other end is sealed to the extremity of inner endconduit 19.

An annular space 21 is provided between the inner wall of rigid tube 17and the outer wall of inner end conduit 19, and is bounded at one end byplug 18. Composite insulation 13 extends into space 21 to contact plug13. The remaining portion of annular space 21 is filled with anadsorbent, preferably calcium zeolite A as disclosed and claimed in U.S.Patent No. 2,882,243, to remove traces of air and Water accumulating inthe insulation space 12. Other suitable adsorbents include silica geland charcoal. It is to be noted that the adsorbent 22 is locatedadjacent to the cold inner end conduit 19 as its capacity is higher atlow temperatures. An alternate method of installing the adsorbentmaterial is to distribute it sparsely along the length of the iiexible,corrugated inner conduit 12 while applying the first layer of compositeinsulation 13. Thus, the adsorbent material 22 is provided incommunicating relationship with the annular insulation space 12.

A sealed capsule 23 formed of glass or other frangible material, andcontaining a suitable amount of active selective hydrogen gettermaterial 24 preferably in a vacuum, is suitably disposed in a getterchamber or protuberance 25 which communicates with the annular adsorbentspace 21. At the desired time, preferably after the space 21 and thecommunicating insulating space 12 have been exhausted by a vacuum pumpor other suitable apparatus, the selective hydrogen getter chamber 25 issuitably deformed as with a pair of pliers or a screw clamp, therebycrushing the glass capsule 23 and exposing the hydrogen selective,active getter material 24- to the communicating spaces 12 and 21. Thecapsule 23 and chamber 25 are preferably held in thermal contact withthe warm wall of rigid tube 17 since the rate of gettering decreaseswith a reduction in temperature. Palladium oxide is the preferredselective hydrogen getter, although copper oxide and metal exchangedzeolitic molecular sieves such as silver exchanged zeolite X are alsosuitable.

As previously mentioned, adsorbents must be maintained at relatively lowtemperatures to achieve high adsorptive capacities. If the presentliexible hose is to be used under circumstances such that the coldservice periods are infrequent or intermittent, it is preferred toemploy an active elemental metal getter such as finely divided barium.Elemental metal getters remove traces of all predominant gases includingmoisture, air and hydrogen, and their gettering capacities are not assensitive to temperature as are the previously discussed adsorbents. Theactive elemental gettering material may for example be used in sealedcapsule 23 instead of the hydrogen selective getter. In this event,space 21 could be eliminated or alternatively filled with the compositeinsulation 13.

The present invention also includes a method of applying flexible,composite insulating matetrial to a curved surface, the compositeinsulation consisting of a multiplicity of radiation impervious barrierssuch as aluminum foil, and low heat conductive fibrous layers such assheets of glass fiber paper or mats. The installation of such compositeinsulating material presents serious problems since the components arethin, rather fragile and do not conform readily to a compound curvature.For example, it has been found that if the insulation is applied assmooth continuous tubes of foil and fiber, even moderate flexing causesthe foils to shorten and draw back from the hose ends as a result ofwrinkling and buckling. This exposes a considerable length of the innerconduit to radiation. More severe exing of continuous foil layers causesthe foils to break or tear, thereby producing Win- Cil dows for radiantheat flow. These problems are overcome by providing the radiationimpervious barriers in elongated strips. As illustrated in FIG. ll, theradiationimpervious strips are helically wrapped without bonding aroundthe curved surface, eg., cylinder 31, from one end to the other endthereof so as to provide an overlap between adjacent edges 32 and 33 ofadjacent helices, e.g., 34 and 35.

The overlapped edges of the helical windings slide one upon the other asthe hose is flexed and this eliminates the foil-shortening problemencountered with continuous foil layers. The degree of overlap isimportant and must be sufficient to prevent spreading the edges of thewindings apart when the hose is flexed to the minimum radius expected inservice. Spreading the windings should be avoided since this opensunshielded areas in the insulation and increases radiation. Furthermorethe separated edges will catch one on the other when the hose is againstraightened thus wrinking or tearing the ribbon edges and producingpermanent radiation windows An overlap of 10% of the strip width isconsidered the minimum for dependable insulation performance, while anoverlap in excess of 30% is unnecessary and should be avoided since itadds excessive heat capacitive material and increases cool-down losses.An `overlap width of about 20% of the radiation impervious strip widthrepresents a preferred balance between heat capacitive mass anddependable insulation performance.

When the curved surface is cylindrical as for example the presentflexible hose, it has been found that the radiation impervious stripshould have a width between f/a and of the cylinder diameter. This rangeis advantageous because the resultant insulation is economicallyapplied, and in the case of the hose, the insulation will possess afiexibility which is approximately matched to the flexibility of thehose.

On completion of helical wrapping the curved surface from end-to-end, afirst radiation-impervious barrier is formed. As illustrated in FIG. 5,a concentric layer 36 of the low heat conductive fibrous material isthen applied around the outer surface of the helically wound firstradiation impervious barrier so as to completely cover the barrier. Thefibrous material layer can, for example, be applied satisfactorily byhelical wrapping or as individual sheets of any convenient length, thewidths of which are at least as great as and preferably equal to thecircumference of the layer being applied. A second, helically woundradiation-impervious barrier is then formed around the outer surface ofthe concentric layer of the low heat conductive fibrous material in thesame manner as the first radiation impervious barrier so as tocompletely cover the low conductive fibrous layer. Thereafter,additional layers of low heat conductive fibrous material and barriersof radiation impervious material are similarly applied in alternatingsequence and in sufcient quantity to achieve a desired degree of thermalinsulation for the curved surface.

As mentioned above, the low-conductive fibrous component of theinsulation may also be applied in the form of strips wound helically toform discrete layers separating the layers of radiation barrier. Whenthe brous component is used in strip form, still another mode ofapplying the composite insulation in concentric layers is possible. Theradiation barrier and fiber strip materials may first be overlaid andthen wound on the conduit as though a single strip. The appearance ofthis construction is shown in FIG. 6 with the thickness of insulationlayers greatly exaggerated for clarity. To avoid contact betweenradiation barriers in adjacent layers, the fiber strip should be widerthan the radiation barrier, and the two strips should be overlaid withmarginal fiber material extending beyond both edges of the radiationbarrier. As illustrated, flexible corrugated inner conduit 10 issurrounded by wire braid 14, and three composite insulation layers 4t),41 and 42 of progressively increasing diameters. Each layer comprises -astrip 43 of low-.conductive fibrous material and a yrelatively narrowerstrip 44 of radiation irnpervious material.

Viewed in cross-section, a curved surface insulated by the presentwrapping method using any of the described techniques results indiscrete concentric cylinders of iusulation components. The radiationbarriers are entirely separate one from another without metalliccontact.

In an alternative method of applying t-his composite insulation, asdisclosed for example in previously referenced copending applicationS.N. 597,947, now U.S. Patent 3,007,596, the component layers may beWound as continuous spirals from the innermost to the outermost layer.Two adjacent shields at any selected point in the insulation are thusconnected metallically by the continuation of the shield around theinsulation layer. While this continuous spiral technique is satisfactoryfor insulating large conduits or tanks, it is not the preferred methodfor small size objects such as the conduits of this invention. This isbecause the heat conduction inward along the spiral shield is sufficientto reduce significantly the temperature difference between layers andthus disturb the temperature gradient through the insulation thickness.For example, in a 3-inch diameter layer heat transmission through theinsulation is theoretically increased more than when spiral, rather thanconcentric shields are used, while in 2-inch and 1inch layer sizes theincrease is more than 40% and 170%, respectively. Furthermore, it isdifficult to employ the overlapping ribbon technique to achieveflexibility when using the continuous spiral method of insulation. Forthe above reasons, the composite insulation is preferably applied asconcentric layers in one of the previously described modes.

This composite insulation assembly method employing concentric layers isparticularly suitable for applying the insulation in annular space I12tbetween the flexible inner conduit 10 and outer jacket 1\1 of ltheflexible hose assembly of this invention. Also the radiation imperviousbarriers of such assembly method are preferably helically wound metallicribbon having a thickness between about 0.002 and 0.2 mm. and a widthbetween 125% and 185% of the conduit diameter. The low heat conductivefibrous component is preferably a permanently precompacted paper, andthe composite insulation is applied with suf'licient tightness toprovide between 40 and 250 shields per inch of thickness, under acompression of less than 0.03 lb. per square inch. Alternatively, thelow heat conductive fibrous component may be a relatively loose web offibers which is preferably compressed sufiiciently during installationto provide between about 5 and 50 radiation shields per inch ofinsulation thickness.

Although preferred embodiments have been described in detail it will beunderstood that modifications and variations may be effected withoutdeparting from the spirit and scope of the invention.

What is claimed is:

As an article of manufacture, a hose comprising an inner conduit; acomposite insulation comprising a multiplicity of elongated overlaidstrips of metallic thermal radiation resisting barriers and low heatconductive fibrous layers with marginal fibrous material extendingbeyond both edges of each metallic thermal radiation resisting barrier,such composite strips being helically wrapped around said inner conduitfrom one end to the other to form a plurality of unbondedhelically-wrapped composite layers such that adjacent turns of thecomposite strips in each helically-wrapped composite layer have unbondedoverlapping edges and such that the metallic thermal radiation resistingbarriers in adjacent helically-wrapped composite layers arenoncontiguus; and a larger outer jacket positioned around the compositeinsulation to concentrically enclose said inner conduit, said largerouter jacket being gas-tightly joined at the ends to said inner conduitto provide a vacuum insulation space therebetween substantially filledwith said composite insulation.

References Cited by the Examiner UNITED STATES PATENTS 1,742,775 1/1930Mallay 138-129 X 1,942,468 l/1934 Andrews 138-111 2,039,781 5/1936Debenedetti 138-121 2,300,547 11/1942 Guarnaschelli 13S-124 X 2,385,4569/1945 Marcy 156-187 2,449,369 9/1948 Doane et al 13S-121 2,640,3326/1953 Keyes 62--15 2,682,292 6/1954 Nagin 156-187 2,766,920 10/1956Rawley 13S-144 X 3,009,601 11/1961 Matsch.

LAVERNE D. GEIGER, Primary Examiner.

LEWIS J. LENNY, Examiner.

